A framework for designing video content browsers that are based on browsing keyframes and are used in digital video libraries is presented. Based on a review of existing ideas and systems, we derive a design space to compare existing browser interfaces and to specify new interface ideas in a more systematic way. This design space is used to illustrate three distinctive video browser interfaces we have developed. Results and analysis of user testing on these browsers are also presented, informing refinements and further insights into video browser design. These browsers have been integrated into an experimental digital video library called Físchlár, currently widely used within our university campus. Obtaining usage information from this system allows us to develop some of the desirable features in future interfaces to digital video libraries.